Electronic devices presently on the market are more frequently providing keyboards or keypads which support alternate input functions such as key chording, multiple input methods, different physical orientations, etc. This results in part from devices becoming physically smaller while at the same time they are adding support for additional functionality.
Typically these alternate input functions are indicated through the use of additional symbols on the keys. As a result, the keys on these devices are often difficult to read. One reason is the visual clutter which results from having multiple symbols on each key and crowding the keys closer together. Another reason is that the size of the symbols themselves are reduced to allow them to fit on the keys. These problems are compounded as smaller devices drive the use of smaller keys. Even when the symbols can be read, there may be user confusion as to which set of symbols is applicable to the function for which the device is currently being used.
It is helpful to visually emphasize one set of symbols over the others so that the appropriate set of symbols is more readily apparent to the user. One method of doing so is to illuminate the set of symbols which is to be emphasized.
One method of providing for separate illumination of separate symbols sets is to provide discrete illumination for each symbol on each key. The illumination may be a separate light source, such as an LED, or a light pipe which directs light from a remote source to the key. Both approaches require a separate physical device (i.e. LED or light pipe) for each symbol requiring illumination. With plural symbols per key, this results in a greater number of light sources than there are keys on the keyboard. Of necessity, these light sources must be smaller than the keys themselves, at least at the interface to the key. Where the light source is relatively bulky, it limits how small the device can be made. Where the light source can be made sufficiently small to not drive the size of the device larger, the light source may become fragile due to reduced component sizes. Light sources capable of providing the requisite lighting levels on an individual key basis may also consume a large amount of the available power relative to the rest of the device.
Exemplary devices to which the present disclosure is relevant include computer keyboards; calculator keypads; remote controls for televisions and stereos; kitchen appliances such as microwave ovens; mobile communication devices and PDAs; mobile and automotive media player devices; and converged mobile devices which combine two or more of these functions.